1. Field of the Invention
The present invention relates to a mobile communication system, in particular, to a CODEC system for use with a base-station controlling unit.
2. Description of the Related Art
FIG. 5 shows a digital mobile communication system according to a first example of the prior art. Here, when a mobile terminal 1a calls a mobile terminal 1b, a CODEC 41a of a base-station controlling unit 3a code-converts audio data of the mobile terminal 1a through a base station 2a into PCM audio data regardless of the attributes of, audio data of the mobile terminal 1a and the mobile terminal 1b. The base-station controlling unit 3a transmits the PCM audio data to a mobile-terminal switching station 5. The mobile-terminal switching station 5 transmits the PCM audio data received from the base-station controlling unit 3a to a base-station controlling unit 3b that accommodates the mobile terminal 1b on the called side. A CODEC 41b of the base-station controlling unit 3b code-converts the PCM audio data received from the mobile-terminal switching station 5 into the audio data with the attributes of the mobile terminal 1b. The base-station controlling unit 3b transmits the resultant audio data to the mobile terminal 1b through a base station 2b.
In this first related art reference, regardless of the attributes of audio data of the mobile terminal 1a on the calling side and the attributes of audio data of the mobile terminal 1b on the called side, the base-station controlling unit 3a on the calling side and the base-station controlling unit 3b on the called side perform a code-converting process one time each (a total of two times).
Next, a second related art reference will be described. In the second related art reference, assuming that a mobile terminal transmits non-audio data such as FAX data to a terminal of the telephone network or another mobile terminal, a code-converting (CODEC) process is performed. When a mobile terminal transmits FAX data to a remote terminal, the mobile terminal on the calling side sets the communication mode to a FAX mode. However, at this point, the mobile terminal on the calling side determines whether the current mode thereof is an audio (telephone) mode or a non-audio (FAX) mode and notifies a relevant base station of the determined mode to the determined result. When the base station has received the notification that communication data is nonaudio data from the mobile terminal, the base station connects the communication data to a non-audio interface other than the audio CODEC interface so as to accomplish a non-audio communication with the terminal on the called side.
In other words, an object of the second related art reference is to simplify hardware of a base station in such a manner that a mobile terminal determines whether or not the current mode is audio data mode or non-audio data mode.
Next, the problems of the above-described related art references will be described.
In the first related art reference, when the attributes of audio data of the mobile terminal 1a on the calling side are the same as the attributes of audio data of the mobile terminal 1b on the called side, the base-station controlling unit 3a on the calling side code-converts audio data (with the attributes common in the mobile terminal 1a and the mobile terminal 1b) into PCM audio data. The base-station controlling unit 3b on the called side code-converts the PCM audio data code-converted by the base-station controlling unit 3a on the calling side into original audio data (with the attributes common in the mobile terminal la and the mobile terminal 1b).
Thus, although the attributes of audio data of the mobile terminal 1a on the calling side are the same as the attributes of audio data of the mobile terminal 1b on the called side, since the code-converting process is performed twice, the delay time of is audio data becomes large. In addition, the quality of audio data deteriorates.
The second related art reference is limited to non-audio (FAX) data communications. Further,
In the second related art reference, since a mobile terminal requires a data type determining circuit that determines whether data transmitted therefrom is audio data or non-audio data and a circuit that notifies a base station of the determined result, the additional circuitry increases the size of the mobile terminal.